October 18, 2013

Real-Life Blood Suckers

We were wondering, how many of us will be dressing up as
vampires this Halloween? These mythical supernatural creatures have stalked
the edges of folklore since ancient times. Now a favourite creepy subject for
authors and film directors, they’ve been drinking the blood of their numerous
victims, and chilling the spines of bookworms and movie audiences around the globe.

But did you know that a surprising number of
real-world creatures actually make their living as vampires? The most obvious
of these are the vampire bats. Their way of feeding, where the main food source is blood, is called hematophagy. Three bat species feed solely on blood: the common vampire bat (Desmodus rotundus); the hairy-legged vampire bat (Diphylla ecaudata); and the white-winged vampire bat (Diaemus youngi). All three are native to South and Central
America.

What is hematophagy?

Hematophagy (haematophagy or hematophagia) is the practice of feeding on blood (from the Greek haima ‘blood’ and phagein ‘to eat’). This lifestyle
usually requires stealth (sucking up the blood of another larger animal
is dangerous business & likely to end in your own demise if you get caught) and is frequently
carried out under the cover of darkness.

Blood is a fluid rich in nutritious proteins and lipids that can
be taken without enormous effort, so hematophagy has evolved as a preferred form of feeding in many small animals. However, because the main component of blood is water, it usually can't provide enough
energy for large predators as a sole food source.

But there are many more species – from all corners of
the animal kingdom – that rely on sucking the blood of another animal. Even
humans do it, in a less direct way: we’re not just thinking about eating black pudding
(a type of sausage incorporating a lot of pig’s blood) here; amongst the African
Maasai, for instance, the practice of drinking the blood of cattle mixed with milk is common.

There are worms, molluscs, insects, fish and even
birds that drink the blood of other creatures, so here is our list of the top
five blood-sucking animals….

Number one has got to be the vampire bat
itself. These bats evolved to drink blood from wild animals across their
Central and South American range, but habitat changes and loss of their typical
food source forced them to switch to domesticated animals – particularly
livestock such as horses and cattle – and even humans. The bite and blood loss
itself is not dangerous but, like many blood suckers, bats are significant
vectors of dangerous diseases. In the case of vampires, this is rabies, which
poses a public-health threat across much of their range.

Number two is the animal with perhaps the scariest way of finding a meal. The candirú is a small parasitic catfish
that lives in the Amazon and Orinoco rivers. Normally, they attack other fish
by swimming into their gills and then latching on for a snack. However, on rare
occasions, they have been known to attack people who have been urinating in the
water, by swimming up the urine stream into their urethra.

Number
three is actually an animal that has long benefited man,
albeit that it can be a nuisance too. The medicinal
leech has been used since ancient times but fell out
of favour in the 19th century when the practice of bloodletting
declined. However, its use in medicine has been revived: because the leech
injects anticoagulants when it bites, it can help reduce clotting, relieve
pressure and spur circulation during and after certain surgical procedures. The
blood thinner hirudin is taken from leeches' salivary glands, and synthetic versions have now
been made with its chemical blueprints.

Surprisingly, some birds have also taken up the
blood-sucking habit. At number four,
we find the vampire finch. Among the
population of different finch species in the Galapagos (made famous by Charles
Darwin) is a certain subspecies that supplements its seed diet with a quick
snack from a seabird. Because it remains in less hospitable arid areas during
the dry season it has evolved the special behaviour of picking at wounds on the
backs of larger birds and lapping their blood. It apparently pecks just enough
to keep the blood flowing but not so much that it disturbs the host.

Numerous insects suck the blood of a wide range of
hosts, including one particular species of moth with a sharp proboscis, as well
as various bugs and a multitude of flies. Perhaps the most notorious is the mosquito, which makes it to number five on our list. Incidentally,
it is only the female flies that suck blood in the case of the mosquito. Again,
this wouldn’t really be a problem for the host animal – other than the itching
and scratching – but mosquitoes and other flies are important disease vectors:
mosquito species are well known for carrying malaria or yellow fever, while the
tsetse fly spreads sleeping sickness.

Finally, although it doesn’t make it to our list
because it doesn’t actually suck blood, the so-called vampire squid deserves an honorary mention. It’s scientific name Vampyroteuthis infernalis means ‘vampire
squid from hell’ and it has been given its own taxonomic order:
Vampyromorphida. This mysterious creature lives in the ocean depths, some
1,000m below the surface, and is only about 15cm long. However, it has the biggest
eye-to-body-size ratio of any animal, with red or blue eyes the size of a large
dog, which helps it to see in the abyss. Like many of its kind it can change
colour and it also exhibits bioluminescence, which means it can glow in the
dark. It derives its name from the cape-like webbing connected to its eight
arms, which it uses as a shield.